This invention relates to a process for treatment and recovery of N-methyl-2-pyrrolidone from an effluent stream in a poly(arylene su1fide) process. In a specific aspect, tho invention relates to a process for removing acidic compounds from N-methyl-2-pyrrolidone which utilizes a thin-film evaporator.
In processes for the recovery of N-methyl-2-pyrrolidone which is used in the production of poly(arylene sulfide), the final process step is the recovery of N-methyl-2-pyrrolidone contaminated with acidic compounds such as phenol, N-methylsuccinimide and dimethylpyrrolidone, and high boiling contaminants. It is desirable to keep acidic impurities in N-methyl-2-pyrrolidone used for poly(arylene sulfide) production to a minlmum since their presence, particularly phenol and N-methylsuccinimide, can upset the stoichiometry of the polymerization reaction and result in the formation of off-specification polymer. Under typical oparating conditions in a fractionation process, N-methyl-2-pyrrolidone will be produced which stil contains acidic impurities above the minimum acceptab1e level or the recovery of specification N-methyl-2-pyrrolidone will be lowered resulting in an uuacceptable loss of N-methyl-2-pyrrolidone.
In U.S. Pat. No. 4,501,902, incorporated herein by reference, there is disclosed a process wherein kettle liquid from an N-methyl-2-pyrrolidone recovery fractionation column containing N-methyl-2-pyrrolidone, acidic compounds and high boiling contaminants is treated with an inorganic compound for removal of acidic contaminants. While the process of U.S. Pat. No. 4,501,902 is an advancement in the art, the process of the invention is a significant improvement and solves a previously unrecognized problem by providing a process for removing the reaction products of the acidic compounds, particularly phenol, with the inorganic compound which are soluble in N-methyl-2-pyrrolidone. These soluble reaction products would foul a typical fractionation column for recovering N-methyl-2-pyrrolidone and result in frequent and costly maintenance, and unacceptable plant downtime.